(1) Field of the Invention
This disclosure relates to an organic light-emitting diode (“OLED”) display.
(2) Description of the Related Art
An OLED display includes a plurality of organic light-emitting elements and a plurality of thin film transistors (“TFT”s), which control the organic light-emitting elements. A TFT includes a plurality of thin films and can be disposed at a lower side of an OLED display, while an organic light-emitting element can be disposed at an upper side of the OLED display. An anode of the organic light-emitting element can be disposed at the lower side of the OLED display, and a cathode of the organic light-emitting element can be disposed at the upper side of the OLED display.
An OLED display may be classified as a top emission type, which emits light upward, and a bottom emission type, which emits light downward. In a bottom emission OLED display, an area where light is emitted is decreased due to the TFTs disposed under the organic light-emitting elements, therefore the top emission type can have a more desirable aperture ratio. Also, a bottom emission OLED display can include a spot due to optical interference, which can occur when light passes through the thin films. A top emission OLED display includes very few thin films on the light path, thus substantially reducing or preventing a spot.
Identifying a suitable transparent material that satisfies the work function requirements for a cathode in a top emission OLED display is difficult. Therefore a very thin film of an opaque metal can be disposed for use as the cathode while allowing for the passage of light. A resistance of a very thin film cathode can be large. To address the high resistance of a thin film cathode, an additional common voltage line for transmitting a common voltage can be disposed on the substrate and electrically connected to the cathode of the organic light-emitting element.
However, manufacturing a common voltage line separately from the cathode can be difficult, and an aperture ratio may be reduced due to the area occupied by the common voltage line.